Television system



Juicy '18, 1939.

R. D. KELL TELEVISION SYSTEM original Filed Jan. 3, 19:53 2 ,sheets-sheet 1 /A/V'NTOE:

July 18, 1939., R. D. KELL I 2,166,2l4

` l 'rEIJsvIsIoNv SYSTEM original Filed Jam.l s, 1933 2 sheets-sheet 2 EAY COMPLETES SCANNING START GF FRAMING IMPULSE y A/SHUTTER STARTS To OPEN GHT 0Ns INTENSITV OF RAY NORMAL E'AY .STARTS SCANNING ACTION Rayaffzz,

@etented duty td, m3@

2,166,214 TELEWSHN SYSTEM Ray lili. Kell, Haddoneid, N. J., assigner to lita dio Corporation oi America, New York, N. Y., a

corporation oit Delaware application January-s, rese, serian No.' cresce Renewed Aprii 8, 1937 17 Claims. (CE. E38-7.2)

operating action, which resides in the fact that, when a moving picture film is the subject for transmission, it is fed through the apparatus with image of the entire picture is projected onto a rectangular area of photosensitive, mosaic screen structure forming part of the tube, and this area is scanned by the cathode ray. That is, in the 25 systems of the prior art, the ray begins to scan the screen when the image of the picture is flashed onto the same, and projection of the irna given band-width for transmission of the picdit.A ture.

There is still another important disadvantage in the cathode ray apparatus proposed heretofore, which is attributed to the operating method wherein an image loi each entire picture is projected ontothe screen structure of the tube continuously during the entire scanning period. The

individual elemental areas of the screen structure,

therefore, are not illuminated for the saine period of time before being scanned by the ray.'

' This condition is manifested at the receiving w station by loss of definition of the received picture and an incorrect relation between the high lights and shadows thereof. Furthermore, in this method of operation, the individual elemenm tal areas of the screen take on another charge after being scanned by the ray. The individual such as when the scene of action ohanges.- This 2@ action results in some degree of blurring of the next frame at the receiving station.

With the foregoing in mind, it is one of the objects of my invention to provide an improved television transmission system, embodying. a cathode '25 ray tube for developing the picture signals, whereby standard motion picture lm can bey trans-y mitted more eiiiciently than has been the case heretofore, and without recourse to the use of a high' speed intermittent; and, also without in 30 curring the various disadvantages referred to.

Other objects and advantages will hereinafter appear.

structure, the values of the respective charges`45 corresponding to the values of light intensity at thecorresponding elemental areas of the picture. During the entire remaining ninety percent of the cycle period the shutter device operates to cut e oi the light from the picture so that the screen 50 structure of the tube is dark, and also,.the ray is at normal intensity and operates during this period to scan the screen structure to neutralize the previously stored charges. This completes the operating cycle. 55

My invention resides in the improved system, apparatus and method of operation of the character hereinafter described and claimed.

For the purpose of illustrating my invention,

5 an embodiment thereof is shown in the drawings,

Fig. 3 is a picture chart, illustrative of the manner of operation in Fig. 1; and

Fig. 4 is a diagrammatic view illustrative of a modification With reference to Fig. 1, the'reierence numeral I0 designates a cathode ray tube for developing picture signals. This tube comprises suitable photosensitive, mosaic screen structure l2 which, for example, may be made up of a great number of minute, photosensitized silver globules supportedfon a metallic base plate and each insulated fromv the latter and from each other. A suitable electron gun I4 operates to develop a ray i6 of electrons and to direct the same at the screen structure. The tube is provided with a grounded anode in the form of a silver coating l1 on the inside surface.

The ray I6 is caused to scan the screen structure during intermittent periods. During the relatively short periods between the intermittent scanning periods, the ray is returned to the initial starting point for the next succeeding scanning action.

Le it be assumed, for example, that there are to be 24 picturesI or frames a secondeach having 180 lines horizontally. For these conditions, the ray is deflected horizontally by coils I8 through which a saw-tooth current Wave is caused to pass at a frequency of 4320 cycles. A suitable generator 20 supplies the current wave for this purpose. lAlso, the ray is deflected vertically by coils 22 through which a saw-tooth current wave is caused to pass at a frequency of 24 cycles. A suitable generator 24 supplies the 24cyc1e current wave for this purpose.

The electron gun I4 is provided with a control electrode or grid 26 by which the intensity of the ray is varied in the manner and for the purpose hereinafter explained.

The object for transmission is a standard motion picture film 28 moved intermittently, at the rate of 24 pictures a second, by a standard intermittent 30. The cam shaft 32 of the intermittent is driven directly from the shaft 34 of a mo tor 3B. 'I'he shaft 34 rotates uniformly at the rate of 24 revolutions a second, and the driving connection to the cam shaft I2 is o'f any suitable type having a drive ratio of 1 to 1.

:o A shutter disc 38 is fixed on the motor shaft and is provided with an opening 40 which extendsy over one-tenth of the circumference, as represented in Fig. 3, and through which the individual pictures of the film are projected onto 5 the screen structure I2.

The shutter opening 40 is given a characteristicshape, as shown in Fig. 2, for the purpose of permitting the maximum amount of light, for each revolution of the disc, to pass through to the screen I2. l

The intermittent 30 operates to move a new picture of the film into position during a quarter of each revolution of the cam shaft 22. During the remaining period of revolution of the cam shaft 32, the new picture, previously moved into .hand cornerthe ray serves no position, remains stationary. As represented in Fig; 3,'therefore, each new picture is moved into position during 90 degrees of each revolution of the cam shaft 32, and remains stationary for the remaining 270 degrees.

The disposition of the shutter opening 40 and the fixed adjustment between the shafts 22 and 34 vare such that the relatively short periods. during which pictures are flashed onto the screen I2, occur during the periods when the pictures are stationary. This is represented in Fig. 3.

For the purpose' of maintaining operation of the-generators 28 and 24 at the respective frequencies of 4320 cycles and 24 cycles, sharp electrical impulses of a given amplitude are developed 'at the frequency of 4320 cycles and, after passing through a suitable amplifier 42, are supplied to the generator 20 and operate to drive the same at this frequency. Also, electrical impulses are developed of greater duration than the horizontal' impulses. and at the frequency of 24 cycles. These are also amplified in the amplifier 42. and are then supplied to the generator 24 to drive the same at the required frequency of 24 cycles.

The adjustment of the generator 24 is auch thatV it does not respond to the impulses for horizontal synchronizing. For the purpose of developing the synchronizi' n impulses, the disc 38 is provided vwith 180 sperE tures 44,' evenly spaced and disposed on thecircumference of a circle concentric with the axis of the shaft 34.

During each from a -suitable apertures to arevolution of the disc .28, light source 48 passes through these photo-electric cell 48 connected to the framing impulses, at the required frequencyv of 24 cycles, for driving the generator.24. These impulses are also amplified in the amplier 42 and then supplied to the generator 24 through a. suitable connection, as indicated. The disposition of the aperture 50 is such that it starts to adadmit light to the screen l2.

VIt will be understood that picture signals are only developed as the ray is deflected horizontally from left to right andvertically from top to bottom. During return deflection of the ray from right to left, horizontally, and also during return.

deiiection of the ray vertically from the lower of the screen to the upper left- I lieiulA purpose in the way of developing picture signals. It is therefore desirable to cut off the ray ilection thereof in both horizontal and vertical directions, and for this and framing impulses are taken from a suitable stage of the amplier 42 and applied by a connection 82 to the control lgrid 28. 'I'he polarity and amplitude of each of these impulses is such as to impart a negative bias 'to the grid 28 which is effective to cu't off the ray so that it will be noneffective with respect to the screen i2.

The operation of my improved system will now be explained, with reference to Fig. 3. From the purpose the synchronizing i during return deba.

e 'arsenic point A clockwise to the point B, the opening il@ is-in position to permit an image of the stationary nlm picture to be projected onto the screen i2. During this period, also, the elongated aperture 5d is effective to develop a framing impulse which drives the generator 2d to edect return defiection vertically of the ray, and, at thesame time, to impart a negative bias to the grid 26 to cut off the ray during this return deflection thereof. At the point B, the shutter cuts off all light to the screen l2. At this point the negative bias on the grid 2li will have been removed to restore the ray to normal intensity. Also, deflection of the ray for scanning the screen begins, and occupies a period from the point B clockwise to the point A. During the scanning period, therefore, the screen 'l2 is dark. At the point C, the intermittent tid starts to move the next nlm into position, and completes this movement at the point D. At the completion of the scanning action, at the point A, the cycle is completed, and at this instant the ray is again cut off by the action of the aperture 5&3, and the shutter opening d starts to admit light to the screen l2.

When an image of each picture is flashed onto the screen if during the relatively short 36-degree period, electrostatic charges are stored on` the screen, the value of the stored charge'at a particular elemental area of the screen being proportional to the value of light intensity at the corresponding elemental area of the picture. As the ray l@ scans the screen during the period BCBA, the charges previously stored are neu- 'tralized to developpicture signals. These signalsare supplied by Way of a connection 5d to a suitable amplier 55. The amplified synchronizing impulses are also supplied to this amplifier from the amplifier d2, and are then passed with the amplified picture signals to a suitable radio transmitter As each picture is flashed onto the screen it, the photoelectric action causes a disturbance in the way of a strong impulse which varies in amplitude with the average light intensity over the screen during the Sti-degreeV period. This impulse passes through the connection 5d and thence to the amplifier 5t and the transmitter et, and if received at a distant point would possibly overload the amplifiers thereat and, at any rate, would interfere with reception. For the purpose of removing this disturbing impulse dur-` ing each revolution of the disc 38, a photoelectric cell Gil is disposed as shown to receive the light from the screen l2, and is connected to the ampliiier 5t* by a connection t2. As each picture is flashed onto the screen l2, therefore, an impulse, corresponding in amplitude and duration to the disturbing impulse referred to, is developed by the cell @il and supplied to the amplifier 56. The connection Si is so made that the polarl ity of the impulse developed by cell Bil is opposite to that of the disturbing impulse coming to the amplifier through the connection l. vThese two impulses, occurring simultaneously, are electrically superimposed on each other in the amplifier 5t and substantially balance out. The impulses developed by the cell 60, therefore, compensate for the disturbing impulses. These compensating impulses might be developed in another way, as shown in Fig. 4. That is, the disc 3B in Fig. 1 may be provided with an opening 6d which admits light to a photoelectric cell liti from a suitable source 68. The shape and position of the opening S13 is such that the compensating impulse has substantially the same shape and dura- -consequent blurring of the `jecting onto said structure an only during spaced tion as the disturbing impulse, and occurs simultaneously therewit Ihis compensating impulse is amplified by a suitable amplifier it, and is sp` plied by way of a connection l2 to the input circuit of the amplifier 5t in'Flg. l. The connection l2 is so made that the polarity of the` compensating impulse is opposite to that of the disturbing impulse at the stage inthe amplifier 5t where these two impulses are superimposed on each other.

From all the foregoing, it will be seen that my improved system has advantages over" those proposed heretofore in the Way-of higher percentage of scanning time per frame which results in increased brilliancy of the received picture and diminution of the band-width`for the same degree of detail, substantially complete discharge of the individual photocells which prevents residual charges after. each scanning period and next frame, and subjection of each individual photocell'to the same period of illumination before discharge by the ray which effects better definition ofthe received plcture and a more nearly correct relation between the high lights and shadows thereof. These important advantages can be attributed to the fact that in my improved television transmitting system and method of operation thereof, an image of a film picture is flashed onto the photosensitive screen for a relatively small part of the operating cycle, after which the screen is cut off and the cathode ray is deilected to scan the screen and discharge the elecv trostatic charges previously stored.

While but one embodiment of my invention has been disclosed, itis seen that modifications, within the conception of those skilled in the art, are possible without departing from the spirit of my invention or the scorie of the claims.

.I claim as mylnvention:

l. In the art of television, the method of operation which comprises developing an electron beam and directing the saine at screen structure for the purpose of developing picture signals, varying the intensity of the beam from e. given maximum value'to a given minimum value and maintaining the beam intensity substantially at the maximum value only during spaced' periods of time, deectingsaid beam to cause the same to scan said structure during said periods, and proimage of the object during only the periods of time substantially between said first-named periods.

. 2. In the art of television, the method of operation which comprises developing an electron beam and directing the same at screen structure for the purpose of developing picture signals, projecting onto said structure an image of the object periods of time, rendering the beam substantially noneective to develop 30 the light to picture signals during said periods, and deflecting said beam to cause the same to scan said structure only during the periods of time substantially between said first-named periods.

3. In the art of television, the method of operation which comprises developing an electron beam and directing the samei at screen structure for the purpose of developing picture signals, first projecting onto said structure an image of the object during only substantially ten percent of the cycle period, and then deilecting said beam to cause the same to scan said structure during only substantially the remainder of the cycle `period for the purpose of developing picture signals."

d. In a television transmitter, a cathode ray i transmitter tube including a globular photo-electric screen, means for projecting upon said screen allight image of the object to be transmitted whereby an electrical image is formed on said screen and whereby an undesired electrical impulse is produced by the total electron emission from said screen, means for producing simultaneously with the production of said undesired impulse a second electrical impulse of opposite polarity to said rst impulse, and means for superimposing said two impulses whereby said undesired impulse is balanced out.

5. In the art of. television, the method of operation for each cycle which comprises projecting ,onto photosensltive screen structure an image of the object for Adeveloping picture signals and to develop an accompanying undesirable electrical impulse,` exposing a photosensltlve device to the light reflected from the active surface of said structure to develop an electrical impulse of opposite polarity to said first-named impulse, and electrically superimposing said impulses one on the other.

6. In the art of television, the method of op- -eration which comprises projecting onto photosensitive screen structure an image of the object, scanning said structure to4 develop picture signais, continuously exposing' a photoelectric device to the light reflected from the Vactive surface of said structure. to develop an electrical effect. and utilizing said effect to control the operating action.

7. In television apparatus for developing picture signals, a cathode ray tube comprising screen structure and 4means for developing a cathode ray and directing the same at said structure, means for projecting an image onto a surface 3f said structure, and means for controlling oparating action of said apparatus, said controlling means including a photosensitive device exposed :o the light reflected from said surface.

8. In television apparatus for developing plc- '.ure signals, a cathode ray tube comprising phoelectric screen structure and means for developing a cathode ray and directing the same at :aid structure, means for projecting an image nto a surface of said structure, means for deiecting said ray to 'cause the same to scan said tructure to develop picture signals, an amplifier or amplifying the picture signals developed, neans for controlling operating action of said ,pparatus, said controlling means including a hotosensitive device exposed ,to the light relected from said surface, and a connection beween said device and said amplifier.

9. In a television transmission system, screen tructure, means for scanning said structure, leans for effecting scanning action of said scaning means during intermittent periods, means ir supporting a moving picture illm, means for nparting movement to the iilm during interlittent periods, means for projecting images of ie individual film pictures onto said structure uring intermittent periods, and timing means for iusing both the scanning periods and the ilimlovlng periods to occur during the periods interaning the image-projecting periods.

10. In a television transmission system, photonsitive screen structure, means for developing cathode ray and directing the same at said ructure, means for causing said ray to scan said ructure during intermittent periods, means for lbstantially cutting olf said ray during intermitnt periods, means for supporting a moving plcre iilm, means for imparting movement to the film during intermittent periods, means for projecting images of the individual film pictures onto said structure during' intermittent periods, and

timing means for causing the ray-cut-otl' periods 1'1. In a television transmission system, photosensitive screen structure, an electron gun for developing a ray of electrons and directing the same at said structure, said gun being provided with a control electrode for controlling the intensity of the ray, means for causing said ray to scan said structure during intermittent periods, means for supporting a moving picture film, means for imparting movement to the illm during intermittent periodsjmeans for projecting images of the individual film pictures onto said structure during intermittent periods, means for developing electrical impulses of polarity and magnitude effective to cut oil said ray and occurring during intermittent periods, a connection between said impulse-developing means and said control electrode for applying said impulses to the latter. and tlming means for causing said image-projecting 'pe'- riods and said impulse periods to occur substantially simultaneously and during the periods intervening both the scanning periods and the iilmmoving periods.

/12. In a television' transmitter at which the,

subject to be transmitted is a moving-picture film, a cathode rayr transmitter tube comprising a light-sensitive, screen made up of a plurality of `capacity elements whereby an electrical image may be stored on said screen, said iilm into position intermittently for projecting a picture i'rame upon said screen, means for projecting a' picture frame upon said screen for a comparatively short period while the film is in said position, means for scanning said screen for a comparatively long period with the cathode ray at the end of said short period whereby picture signals are' developed. said scanning also taking place while said nlm ls being moved into position for projecting the next picture frame upon said screen.

13. In a television transmitter at which the subject to be transmitted is a moving-picture nlm, a cathode ray transmitter tube comprising an electron emissive screen made up of a plurality of capacity elements whereby an electrical image may be stored on said screen, means for projecting a picture frame of said film upon said screen for a comparatively short period while the lm is stationary, means for scanning said screen for a comparatively long period with the means for moving l cathode ray at the end'of said short period whereby picture signals are developed, and means including an intermittent device for moving said lm into position for projection of the next picture frame upon said screen during said scanning whereby the cycle of operation may be repeated for said next fraxnfe.

` 14. In a television transmitter at which the subject to be transmitted is a moving-picture lm, a cathode ray transmitter tube including a light-sensitive screen which comprises a plurality of capacity elements whereby an electrical image may be stored on said screen, an intermittent device for moving said film into` position periodically for projecting a picture frame upon said screen, means including a light source for projecting a picture frame upon said screen, a shutter positioned to intercept the light from said source pesaid short period 'whereby picture signals are de-v veloped, said long period including the period during which said intermittent device moves said lm into position for projecting the next picture frame upon said screen.

15. The invention, according to claim 14, characterized in that said shutter and said shutter operating means are so designed that said short period is between 3 and 15 percent of a complete operating cycle including both of said periods.

16. 'Ihe invention; according to claimv14, characterized in that said shutter is a rotatably mounted disc .which has an opening therein of 'such size that said short period is between 3 and 15 percent of a complete operating cycle yincluding .both of said periods.

` 17. In a television transmitter for transmitting pictures from a moving-picture film, a transmitter tube in which there is a light-sensitive screen hav-` ing a. plurality of capacity elements and inwhich there is means for producing a cathode ray, means for projecting the image of a picture frame of said film upon said screen for a certain period while the lm is stationary whereby an electrical image is stored thereon, means for scanning said screen at the end of said period with said cathode ray to develop picture signals, and means for moving said lm into position during said scanning for projecting the image of the next picture frame upon said screen.

RAY D. KELL. 

